If you go to the mirrors page you’ll see cdimage.debian.org under Sweden and it’s an http link. My guess is that the link is just misconfigured on the home page. It’s helpful to avoid https for things like this because it allows you to download updates on machines with outdated security software, eg TLS 1.0/1.1.
I think a lot of the problem is every tutorial expects Fedora/RedHat/Ubuntu/Debian and it’s easy to figure out which instructions are compatible with your distribution, but there isn’t a good knowledge base for Fedora Atomic or related OS. I have a Bazzite VM. Normally I use Ubuntu and am familiar with RHEL compatible, but am constantly lost with Bazzite, trying to use the wrong instructions.